<!doctype html> 
<html> 
<head> 
<meta charset="UTF-8"> 
<title>注册系统</title> 
<style type="text/css"> 
form { 
  text-align: center; 
} 
</style> 
</head> 
<body> 
  
  <form action="register.php" method="post" name="form_register"
    onsubmit="return check()"> 
    用户名<input type="text" name="username" id="username"><br> 
    密码<input type="password" name="password" id="password"><br> 
    确认密码<input type="password" name="assertpassword" id="assertpassword"><br> 
    <input type="submit" value="注册"> 
  
  </form> 
  
  <script type="text/javascript"> 
    function check() { 
      var username=document.getElementById("username").value; 
      var password=document.getElementById("password").value; 
      var assertpassword=document.getElementById("assertpassword").value; 
      var regex=/^[/s]+$/; 
        
      if(regex.test(username)||username.length==0){ 
        alert("用户名格式不对"); 
        return false; 
      } 
      if(regex.test(password)||password.length==0){ 
        alert("密码格式不对"); 
        return false;     
      } 
      if(password!=assertpassword){ 
        alert("两次密码不一致"); 
        return false; 
      } 
    } 
  </script> 
</body> 
</html>